In general, underwater robotics poses certain unique challenges that render many of the principles of terrestrial robotics problematic. A robot underwater is able to move along six degrees of freedom, and maneuvering with six degrees of freedom creates serious complications. A computationally straightforward task of pose maintenance on land becomes far more challenging under water, because of environmental factors such as strong currents in marine environments. Infra-red sensors lose some of their effectiveness in water as well. Wireless radio communications are also impossible over a large distance in water compared to ground based control. All these issues make underwater robotics problems more difficult than terrestrial robotics.
The traditional approach used to propel undersea vehicles is by using propellers or thrusters. Although simple by design, these vehicles lack the maneuverability and agility seen in fish and other marine species. In addition, thrusters are not an energy efficient approach to station keeping underwater.
In computer vision, visual tracking is the process of repeatedly computing a position of a feature or sets of features in a sequence of input images. A number of methods for visual tracking in a dry environment (i.e. not underwater) based on the color of the target are known. One of the known approaches is color-blob tracking, where the trackers segment out sections of the image that match a threshold level for the given target and based on the segmentation output, tracks the shape, size or centroid of the blob, among other features. Another approach is the matching of color histograms, which are a measure of color distribution over an image. Some of the tracking methods are combined with statistical methods to provide more accurate results, one example being mean-shift tracking algorithms, which attempt to maximize the statistical correlation between two distributions. However, the tracking of objects in a dry environment is very different from the tracking of objects underwater. Underwater, vision is impaired by the turbidity of the water caused by floating sedimentation (“aquatic snow”) and other floating debris. The behavior of the light beams is altered by many factors including refraction, which is influenced by waves and water salinity level, scattering, which causes a reduction of contrast between objects and influences color hues, and absorption, which is frequency dependent and makes detection of certain colors difficult. As such, vision in underwater environments has rarely been examined due to the complications involved.